/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Creator:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2006, by Barak Naveh and Contributors.
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation,
 * Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */
/* --------------------------
 * DirectedNeighborIndex.java
 * --------------------------
 * (C) Copyright 2005-2006, by Charles Fry and Contributors.
 *
 * Original Author:  Charles Fry
 *
 * $Id: DirectedNeighborIndex.java,v 1.2 2007/05/22 15:52:53 kjellw Exp $
 *
 * Changes
 * -------
 * 13-Dec-2005 : Initial revision (CF);
 *
 */
package org.jgrapht.alg;

import java.util.*;

import org.jgrapht.*;
import org.jgrapht.alg.NeighborIndex.*;
import org.jgrapht.event.*;

/**
 * Maintains a cache of each vertex's neighbors. While lists of neighbors can be
 * obtained from {@link Graphs}, they are re-calculated at each invocation by
 * walking a vertex's incident edges, which becomes inordinately expensive when
 * performed often.
 * 
 * <p>
 * A vertex's neighbors are cached the first time they are asked for (i.e. the
 * index is built on demand). The index will only be updated automatically if it
 * is added to the associated graph as a listener. If it is added as a listener
 * to a graph other than the one it indexes, results are undefined.
 * </p>
 * 
 * @author Charles Fry
 * @since Dec 13, 2005
 */
public class DirectedNeighborIndex<V, E> implements GraphListener<V, E> {
	// ~ Instance fields
	// --------------------------------------------------------

	Map<V, Neighbors<V, E>> predecessorMap = new HashMap<V, Neighbors<V, E>>();

	Map<V, Neighbors<V, E>> successorMap = new HashMap<V, Neighbors<V, E>>();

	private DirectedGraph<V, E> graph;

	// ~ Constructors
	// -----------------------------------------------------------

	/**
	 * Creates a neighbor index for the specified directed graph.
	 * 
	 * @param g
	 *            the graph for which a neighbor index is to be created.
	 */
	public DirectedNeighborIndex(DirectedGraph<V, E> g) {
		graph = g;
	}

	// ~ Methods
	// ----------------------------------------------------------------

	/**
	 * Returns the set of vertices which are the predecessors of a specified
	 * vertex. The returned set is backed by the index, and will be updated when
	 * the graph changes as long as the index has been added as a listener to
	 * the graph.
	 * 
	 * @param v
	 *            the vertex whose predecessors are desired
	 * 
	 * @return all unique predecessors of the specified vertex
	 */
	public Set<V> predecessorsOf(V v) {
		return getPredecessors(v).getNeighbors();
	}

	/**
	 * Returns the set of vertices which are the predecessors of a specified
	 * vertex. If the graph is a multigraph, vertices may appear more than once
	 * in the returned list. Because a list of predecessors can not be
	 * efficiently maintained, it is reconstructed on every invocation by
	 * duplicating entries in the neighbor set. It is thus more efficient to use
	 * {@link #predecessorsOf(Object)} unless duplicate neighbors are required.
	 * 
	 * @param v
	 *            the vertex whose predecessors are desired
	 * 
	 * @return all predecessors of the specified vertex
	 */
	public List<V> predecessorListOf(V v) {
		return getPredecessors(v).getNeighborList();
	}

	/**
	 * Returns the set of vertices which are the successors of a specified
	 * vertex. The returned set is backed by the index, and will be updated when
	 * the graph changes as long as the index has been added as a listener to
	 * the graph.
	 * 
	 * @param v
	 *            the vertex whose successors are desired
	 * 
	 * @return all unique successors of the specified vertex
	 */
	public Set<V> successorsOf(V v) {
		return getSuccessors(v).getNeighbors();
	}

	/**
	 * Returns the set of vertices which are the successors of a specified
	 * vertex. If the graph is a multigraph, vertices may appear more than once
	 * in the returned list. Because a list of successors can not be efficiently
	 * maintained, it is reconstructed on every invocation by duplicating
	 * entries in the neighbor set. It is thus more effecient to use {@link
	 * #successorsOf(Object)} unless dupliate neighbors are required.
	 * 
	 * @param v
	 *            the vertex whose successors are desired
	 * 
	 * @return all successors of the specified vertex
	 */
	public List<V> successorListOf(V v) {
		return getSuccessors(v).getNeighborList();
	}

	/**
	 * @see GraphListener#edgeAdded(GraphEdgeChangeEvent)
	 */
	public void edgeAdded(GraphEdgeChangeEvent<V, E> e) {
		E edge = e.getEdge();
		V source = graph.getEdgeSource(edge);
		V target = graph.getEdgeTarget(edge);
		getSuccessors(source).addNeighbor(target);
		getPredecessors(target).addNeighbor(source);
	}

	/**
	 * @see GraphListener#edgeRemoved(GraphEdgeChangeEvent)
	 */
	public void edgeRemoved(GraphEdgeChangeEvent<V, E> e) {
		E edge = e.getEdge();
		V source = graph.getEdgeSource(edge);
		V target = graph.getEdgeTarget(edge);
		if (successorMap.containsKey(source)) {
			successorMap.get(source).removeNeighbor(target);
		}
		if (predecessorMap.containsKey(target)) {
			predecessorMap.get(target).removeNeighbor(source);
		}
	}

	/**
	 * @see VertexSetListener#vertexAdded(GraphVertexChangeEvent)
	 */
	public void vertexAdded(GraphVertexChangeEvent<V> e) {
		// nothing to cache until there are edges
	}

	/**
	 * @see VertexSetListener#vertexRemoved(GraphVertexChangeEvent)
	 */
	public void vertexRemoved(GraphVertexChangeEvent<V> e) {
		predecessorMap.remove(e.getVertex());
		successorMap.remove(e.getVertex());
	}

	private Neighbors<V, E> getPredecessors(V v) {
		Neighbors<V, E> neighbors = predecessorMap.get(v);
		if (neighbors == null) {
			neighbors = new Neighbors<V, E>(v, Graphs.predecessorListOf(graph,
					v));
			predecessorMap.put(v, neighbors);
		}
		return neighbors;
	}

	private Neighbors<V, E> getSuccessors(V v) {
		Neighbors<V, E> neighbors = successorMap.get(v);
		if (neighbors == null) {
			neighbors = new Neighbors<V, E>(v, Graphs.successorListOf(graph, v));
			successorMap.put(v, neighbors);
		}
		return neighbors;
	}
}

// End DirectedNeighborIndex.java
